1. Field of the Invention
The present invention relates to a positioning apparatus for positioning a movable member, and more particularly, it relates to a positioning apparatus used with a sheet feeding system of a copying machine, printer and the like. Particularly, the present invention relates to a positioning apparatus including a movable member for permitting the guide of a plurality of kinds of sheets having different widths.
2. Related Background Art
In the past, in order to permit the guide of sheets having different widths, in an apparatus such as a copying machine, a mechanism for positioning the sheet in its transverse (width) direction included a sensor disposed reference position regarding the positioning of the sheet so that the movable member returned to the reference position was detected by the sensor to stop a stepping motor. And, when a sheet having a different width was sent to the positioning mechanism, the stepping motor was driven again under the time control or pulse control to shift the movable member from the reference position to a predetermined position, thus positioning the movable member with respect to the sheet to be guided.
However, in such conventional positioning mechanism, since, for example, a photo-interrupter is used as the sensor arranged at the reference position and a width of each slit of such photo-interrupter is about 0.5 mm, the error at the reference position is at least 0.5 mm or more. Further, since the error in the attachment of the sensor, angular error in the stepping motor, dimensional error in the movable member and the like are added, the positioning error will be greater.
In an image forming apparatus such as a copier or the like, to enhance the accuracy of the position at which an image is formed, the positioning of the sheet is effected in a main scanning direction. However, when the aforementioned conventional positioning mechanism is used, the positioning error is too great to position the movable member correctly, as mentioned above, thus arising a problem that the deviation of the image from the correct image forming position is noticeable.